In a refrigeration system which draws air from a served space through an evaporator coil, and which discharges conditioned air back into the served space, the position and condition of a controlling temperature sensor is critical. This is especially true for a transport refrigeration system, which is usually controlled in response to the temperature of air returning to the evaporator coil. The return air temperature sensor is located in a lower portion of the served space. If the return air temperature sensor is improperly positioned, or pushed or forced out of position, such as during loading of the served space, or subsequent shifting of the load, the temperature of the served space will not be controlled to the desired temperature range adjacent to a selected set point temperature SP, and damage to the load may occur. A return air temperature sensor which has drifted out of an allowable tolerance will present the same problem.
Thus, it would be desirable, and it is an object of the present invention, to be able to detect when a return air temperature sensor is not responding correctly to air returning to an evaporator coil of a refrigeration system from a served space, due either to incorrect positioning of the return air sensor in the return air flow path, or to drifting of the return air temperature sensor out of an allowable tolerance.